The invention relates to a method of transmitting data in a telecommunications exchange, such as a telephone PBX, which has a data transmission line system, which can be an optical data transmission line system, with various connection stations, such as subscriber stations, connection line sets and terminal devices. The various connection stations for information transmission between at least two connectable connection stations, may possess different traffic flow properties in respect of the quantity and speed of the data transmission and in respect of the transmission process--for example continuous (stream) transmission process and/or burst process. Also, at least the first process is based on the time slot process where periodically recurring time slots are combined to form a pulse frame which transmits a specific quantity of data in a predetermined period of time (for example 1024 bits in 125 microseconds). The time location is clearly defined for this quantity, and the items of data which are transmitted in the various processes are exchanged via a common data transmission line group which is connected to all the various connection stations such as subscriber stations, connection line sets and terminal devices, for which purpose via the data transmission line group an uninterrupted sequence of storage volume, defined by start and end characteristics and corresponding to the pulse frame, can be continuously made available to the connection stations.
In data transmission line systems to be used in communications technology, for example optical data transmission line systems especially for so-called local area networks (LAN), subscribers and devices must be connected which possess highly differing traffic flow properties. When fully digital terminal devices, for example, telephone stations, video devices and the like are connected, items of data information must be transmitted continuously. In addition however, with regard to automated office communications, terminal devices must be connected which produce intermittent traffic flow. These devices consist, for example, of high-resolution graphic terminals, data bank processors, and text terminals. These devices require a transmission capacity of several megabits per second (MBit/s), for fractions of seconds.
An article by P. Zafiropoulo and E. H. Rothauser in proceedings ICCC, 1972, pages 309 to 315, described how a continuous (stream) transmission process and a burst process can be used in ring systems. In the system described therein the allocation of the time slots for the continuous transmission process is carried out by observing a "busy" bit contained in each time slot. A station which is ready for transmission discovers a free time slot and then inserts the target address of the receiver into this time slot. If the receiver is not engaged it responds in the same time slot with an appropriate item of information so that a connection is established via this time slot. However, this signalling in the time slot has the disadvantage that less space or no space is available during the established connection for the signalling activities which are necessary in state of the art digital communication systems. In addition the disadvantage exists that the transmission capacity is further impaired by the accomodation of the aforementioned "busy" bit and the sender address and target address in each time slot. In order to transmit data parcels in this system, it is necessary to provide a separate data transmission line group where the access takes place in the same way with a "busy" bit. This system is not successful in state of the art digital communications in combining the continuous (stream) transmission process with the burst process for transmission via a data transmission line group.
An article by I. Favre in "Proceedings International Conference on Local Computer Networks" 1982, Florence, pages 23 to 37, discloses how a time slot frame can be divided into two sub-frames for an optical ring system. Here the first sub-frame serves as the frame for the continuous transmission of information items, whereas data bursts are transmitted in the second frame. The second sub-frame is allocated by means of a control array which is continuously accommodated in this channel and which contains information as to whether the data array of the sub-frame in question is free or engaged. Only when a free characteristic exists can a data burst be input. Thus in this process each sub-frame must contain a free/engaged characteristic of this type and the address of the transmitting station and of the target must be added. This also results in the unnecessary loss of a large quantity of storage capacity.
European patent application No. 0 054 077 discloses a process which does not use a frame-synchronous time slot structure, but in which information items are transmitted continuously and in bursts. Here access is provided by means of the transmission of an item of access entitlement information via the data transmission line group, and this is done in such a way that a station which is ready for transmission can transmit when it receives this access information. When this occurs a data burst can be transmitted from this station. Continuous data items can be transmitted only in restricted form in this process since in the event of heavy traffic loading periodic access within a prescribed period of time is not guaranteed. The larger the data burst for non-continuous traffic, the greater the time shift. As a result speech traffic for long distance conversations can, for example, become impossible. In order to nevertheless ensure continuous traffic, an additional monitoring circuit is required in this system. On the basis of requests from the stations transmitting the continuous information items, this monitoring circuit ensures that at periodic intervals it is possible to interrupt the normal access for the transmission of data bursts. Then, in place of the normal access information, a special item of information is transmitted which ensures access only to those stations having a continuous traffic flow.